
This application claims the benefit of Korean Patent Application No. 1998-31991, filed on Aug. 6, 1998, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD), and more particularly, to a semitransparent reflective type LCD which operates both as a transmitting type LCD and a reflective type LCD.
2. Discussion of the Related Art
A liquid crystal display device (LCD) has been widely used for a display device of a portable television and a notebook computer. The liquid crystal display device is classified into two types. One is a transmitting type liquid crystal display device using a backlight as a light source, and the other is a reflective type liquid crystal display device using an external light source such as sunlight and an indoor lamp. It is difficult to decrease the weight, the volume, and the power consumption of the transmitting type LCD because of the backlight. On the other hand, the reflective type LCD has an advantage of not needing to use the backlight, but it cannot operate without the external light source.
In order to overcome the drawback of the two type LCDs, a semitransparent reflective type LCD which can operate both as reflective and transmittance type LCDs is disclosed in the U.S. Pat. No. 5,742,112.
FIG. 1 is a sectional view showing a portion of the semitransparent reflective type LCD, where a thin film transistor (not shown) is the switching element. As shown in FIG. 1, a backlight 3 is provided under a first substrate 1 as a lower substrate, and a first polarizer 2 is provided between the backlight 3 and the first substrate 1 to linearly polarize light from the backlight 3. Further, the first substrate 1 is provided with a semitransparent reflecting electrode which is connected to a drain electrode of a thin film transistor and has opening and recessed portions 13 and 14. A first alignment layer 5 is formed on the semitransparent electrode 4.
A scattering film 12 is formed over a second substrate 9 as an upper substrate to scatter the light, and a second polarizer 11 is formed between the scattering film 12 and the second substrate 9. A phase retardation film 10 is formed between the polarizer 11 and the second substrate 9 to change the polarization direction of the light by optical anisotropy. A transparent electrode 8 as a counter electrode to the reflecting electrode 4 is formed on an inner surface of the second substrate 9, and a second alignment layer 7 is formed thereon. A liquid crystal layer 6 is formed between the two substrates 1 and 9 to control the light polarization by changing the crystal structure of its LC molecules according to the voltage of the reflecting electrode 4.
When there is a bright external light, the semitransparent reflective type LCD operates as a reflective type LCD which uses the external light as a light source without using the backlight 3. The reflected light on the reflecting electrode 4 is scattered in various directions by the scattering film 12 to enlarge the viewing angle range of the user.
When there is no bright external light, the semitransparent reflective type LCD operates as a transmitting type LCD in which light from the backlight 3 enters the liquid crystal layer 6 through the opening and recessed portions 13 and 14.
The semitransparent reflective type LCD has a low power consumption in comparison with the conventional transmitting type LCD because the backlight 3 is not used when there is a bright external light. Further, in comparison with the reflective type LCD, the semitransparent reflective type LCD has an advantage that it can operate as a transparent type LCD using the backlight 3 when there is no bright external light source.
However, when the semitransparent reflective type LCD operates as a reflective type LCD, the incident light is not sufficiently reflected due to the opening and recessed portions 13 and 14, which causes defects due to black spots. Therefore, when used as a reflective type LCD, the semitransparent reflective type LCD has a low reflectance in comparison with the general reflective type LCD.
Accordingly, the present invention is directed to a semitransparent reflective type liquid crystal display device that substantially obviates the problem due to limitations and disadvantages of the related art.
An object of the present invention is to provide a semitransparent reflective type LCD having an improved light reflectance in the main viewing angle direction.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve the object of the present invention, the present invention provides a semitransparent reflective type LCD which comprises first and second substrates facing to each other; a backlight on an outer surface of the first substrate; an uneven layer being on an inner surface of the first substrate and having an uneven surface; a reflecting electrode being along the uneven surface and having a transparent portion substantially facing in a main viewing angle direction which is defined as a direction where the user""s eye is mainly positioned; and a liquid crystal layer between the first and second substrates.
A semitransparent reflective LCD of the present invention has the following advantage. The transparent portion is in an inclined surface facing the main viewing angle direction. Accordingly, when operating as a reflective type LCD, the quantity of the main external light which is incident on the transparent portion is decreased to prevent the black spot defect and then increase the light reflectance.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.